Not Applicable.
The present invention is related generally to ultrasonic imaging systems, and in particular to an ultrasonic imaging system utilizing scalable architecture permitting synthetic focus images to be generated in real-time.
Ultrasonic imaging systems are used in a wide range of applications ranging from fetal imaging to non-destructive evaluation. In developed countries, almost every fetus is imaged using ultrasonic imaging to monitor growth and development and to evaluate fetal health. Medical ultrasound systems are used in a wide variety of medical applications, ranging from cardiac evaluation to intra-operative neurosurgery for tumor location to breast cancer screening. Some example of non-medical uses of ultrasonic imaging systems include the location of faults in structures such as steel beams and aircraft wings, seismic imaging for mineral exploration, and synthetic-aperture radar for defense and commercial applications.
Unlike magnetic resonance imaging (MRI) or computer tomography (CT) systems, ultrasonic imaging systems provide real-time images. The generation of real-time images renders ultrasonic imaging systems attractive for many applications. In addition, when compared to MRI or CT systems, ultrasonic imaging systems are much lower in cost, and, as such, are the preferred method for imaging when cost is a concern (as it is in screening applications where large populations need to be imaged). Ultrasonic imaging uses non-ionizing radiation, unlike CT imaging systems, and is thus considered to have far fewer risks, especially when used over a period of many years as a screening method.
Traditional array-based ultrasonic imaging systems use a xe2x80x9cfocus and steerxe2x80x9d method for forming images. In the xe2x80x9cfocus and steerxe2x80x9d method, an ultrasonic beam is focused to transmit and receive at selected image points or pixels. For real-time operation, typically about 100 pixels are in focus. Producing a focus and steer image which is in exactly in-focus at each image pixel requires a data acquisition time which is the product of the number of image pixels and the round-trip time of the ultrasonic wave.
For acceptable image sizes, the data acquisition time using the xe2x80x9cfocus and steerxe2x80x9d method in an ultrasonic imaging system is so large that it is impractical to form real-time images which are in focus at each image pixel. Hence, in a system utilizing xe2x80x9cfocus and steerxe2x80x9d methods, absolute focus of each pixel in the image is compromised in order to achieve real-time frame rates.
An alternative to xe2x80x9cfocus and steerxe2x80x9d methods in ultrasonic imaging, known as synthetic focus imaging, uses the complete dataset of image data. All transmitter-receiver array element pairs are used to acquire ultrasonic backscatter data. The data acquisition time for a synthetic focus imaging approach to the generation of ultrasonic images, which are in-focus at each pixel, is short enough to support real-time imaging for acceptable image sizes, e.g., 512 by 512 pixels. The computation requirements, however, for synthetic focus imaging are very large.
Synthetic focus imaging offers the possibility of providing for early detection and staging of cancers, especially for static, easy to insonify glands like breast and prostate tissue. Cancers in these tissues are among the leading causes of new cancer cases. Ultrasonic imaging is currently utilized to detect and stage these cancers, but the systems are limited by resolution and contrast capabilities. Synthetic focus imaging systems separate data acquisition from image formation and can provide in-focus information at every image pixel. This permits image contrast to be easily adjusted to compensate for various properties of the tissues being examined. However, current synthetic focus imaging systems have relatively long image-formation time. This is due to the fact that the synthetic-focus image acquisition time is proportional to the number of ultrasonic transducers in the transmit/receive array. Conversely, the time required for image formation using convention focus-and-steer configurations is proportional to the number of focal points in the image. Therefore, since the number of pixels in an image is typically orders of magnitude greater than the number of transducers, acquiring an in-focus image with conventional systems is impractical.
In synthetic-focus imaging systems, the following computation is required to calculate a single pixel p(i,j) using data from an N element transducer array (N sources and N sensors). TOF(i, j, m, n) is the time-of-flight contribution to pixel p(i,j) from source m and sensor n:       p    ⁡          (              i        ,        j            )        =            ∑              m        =        1                    m        =        N              ⁢                  ∑                  n          =          1                          n          =          N                    ⁢              f        (                  TOF          ⁡                      (                          i              ,              j              ,              m              ,              n                        )                          )            
The time needed to generate an image can be broken down into the following principal tasks: (1) time-of-flight (TOF) calculation; (2) retrieval of backscattered signals from memory; and (3) summation of backscattered values to define each pixel value.
Linear array and phased array ultrasonic imaging systems that use the traditional xe2x80x9cfocus and steerxe2x80x9d method for forming real-time images are common. To date, however, there has not been a real-time synthetic focus ultrasonic imaging system developed which captures images large enough to be used for diagnostic purposes. Synthetic focus ultrasound images have been formed using data acquisition hardware and off-line computation engines, including single processor and multi-processor computer systems. However, none of these systems is capable of achieving real-time synthetic focus image generation using the complete data set of image pixels for reasonable sized images.
A method for computing, in real-time, the time-of-flight surfaces required to form synthetic focus images is described by S. R. Broadstone and R. M. Arthur in xe2x80x9cxe2x80x9cAn Approach To Real-Time Reflection Tomography Using The Complete Datasetxe2x80x9d, in proceedings 1986 Ultrasonics Symposium, Vol. 86CH2375-4, pp. 829-831, IEEE Press, 1986, (the Broadstone and Arthur reference). The Broadstone and Arthur reference further describes an integrated circuit implementation of the disclosed method. In the integrated circuit design, one time-of-flight calculator is required for each transmit/receive transducer pair in a massively parallel ultrasonic imaging system in order to form real-time synthetic focus images. However, the Broadstone and Arthur reference does not provide a complete, realizable architecture for a synthetic-focus imaging system capable of being constructed using currently available integrated circuit components or technologies.
Current ultrasonic imaging systems which utilize the xe2x80x9ccomplete data setxe2x80x9d for image formation require large numbers of components per channel for data storage and image generation. These hardware requirements would be exacerbated in the implementation of a real-time imaging system, and, for this reason, none have been constructed.
Accordingly, there is a need for a real-time synthetic-focus ultrasonic imaging system which exploits parallelism to facilitate data storage and image generation, which is capable of producing images of a size which are sufficiently useful for diagnostic purposes, and which permits adaptive image generation through iterative image processing to simultaneously extract sample properties and improve image quality.
Briefly stated, the present invention provides an apparatus for use in an ultrasonic imaging system adapted for generating synthetic focus images in real-time. The apparatus employs a parallel processing integrated circuit architecture which is scalable and can be employed to construct real-time synthetic focus ultrasonic imaging systems having a large number of transducer array elements. The apparatus provides the ability to quickly and iteratively generate candidate final images based on a single complete dataset of image pixels, and facilitates the development of optimization techniques for accurate speed of sound extraction.
In one embodiment, the architecture of the ultrasonic imaging system of the present invention employs a single field-programmable gate array (FPGA) or ASIC for data storage and sub-image generation for each transducer pulser/receiver channel. The FPGAs are configured with on-chip block memories to store digitized return echo data, and optionally with one or more block memories which are configured to hold data associated with each transmitter receiver pair in the ultrasonic imaging system. Additional logic inside each FPGA is used to calculate memory addresses during image generation to generate the time-of-flight surfaces and to form required sub-images, which are in-turn, combined to produce a completed ultrasonic image.
A method of the present invention propagates ultrasonic energy towards a sample object and receives the reflected echoes. The received echoes are digitized and stored, and subsequently utilized with one or more coefficients to generate an ultrasonic image of the sample object. By altering the coefficients, adaptive image generation from the complete set of image pixel data facilities the generation of subsequent images having varied focus or contrast from the initial image.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.